Effects of cobalt ion doped in the ZnS passivation layer on the TiO2 photoanode in dye sensitized solar cells based on different counter electrodes

- Doped- ZnS on the TiO2 surface is efficient approach for increase efficiency.
- Doping of Co2+ ion leads to the creation of the midgap states in the ZnS.
- The midgap states improve the charge transfer at the photoanode.

In this study, effect of Co2+ ion incorporation into ZnS passivation layer on TiO2 has been investigated in dye sensitized solar cells (DSSCs), which has been used to improve the photovoltaic performance. Co2+ doped ZnS layer has been successfully fabricated using the successive ionic layer adsorption and reaction (SILAR) method on the surface of the TiO2 nanoparticles in the DSSCs based on an organic dye. Two high performance counter electrodes (Pt and CoS) have been applied in the DSSCs and their performances have been studied. The DSSCs based on ZnS coated TiO2 photoanode with Pt and CoS CEs attained a power conversion efficiency of 2.13% and 2.10%, respectively. By doping ZnS with cobalt ion in the fabricated device based on 2-cyano-3-(4-(diphenylamino)phenyl) acrylic acid (TPA) sensitizer with Pt CE, the efficiency of 2.60% obtains at an irradiation of AM 1.5 and about 33% increase in efficiency are observed compared to the cell based on bare TiO2. Also, an efficiency of 2.40% is observed for DSSC based on CoS CE, showing 33% enhancement in efficiency by applying Co-doped ZnS layer compared to the standard cell. The existence of Co ions in the Co-doped ZnS/TiO2 film has been detected by energy dispersive X-ray spectroscopy (EDS). The optical property of Co-doped ZnS nanoparticle film has been studied by UV-vis absorption spectroscopy. The electrical property of Co-doped ZnS/TiO2 DSSCs has been studied by electrochemical impedance spectroscopy (EIS) under air mass 1.5 condition. The results indicate that passivation layer doped with metal ion in the photoanode is as a simple and effective method for optimizing the electron transport that enhancing photocurrent and thereby power conversion efficiency in the DSSCs.